Alpha-Amylases (alpha-1,4-glucan-4-glucanohydrolases, E.C. 3.2.1.1) constitute a group of enzymes, which catalyze hydrolysis of starch and other linear and branched 1,4-glucosidic oligo- and polysaccharides.
Amylases can be used commercially in the initial stages (liquefaction) of starch processing; in wet corn milling; in alcohol production; as cleaning agents in detergent matrices; in the textile industry for starch desizing; in baking applications; in the beverage industry; in oilfields in drilling processes; in deinking of recycled paper and in animal feed.
Alpha-amylases are isolated from a wide variety of bacterial, fungal, plant, and animal sources. Many industrially important α-amylases are isolated from Bacillus sp., in part because of the generally high capacity of Bacillus to secrete amylases into the growth medium. Furthermore, there is a need for blends of alpha-amylases, or variants thereof, which can capitalize on the best properties of at least two alpha-amylases from at least two bacterial strains.
For example, alpha-amylases isolated from B. stearothermophilus (AmyS) have been used in fuel ethanol applications because of rapid viscosity decreasing property. Fuel ethanol plants have 20-30 min of slurry time before slurry goes through the jet cooking step and in that 20-30 min viscosity has to be broken down for trouble-free pipe flow. However, certain alpha-amylases or variants thereof are not thermostable, so while they decrease the viscosity of a slurry over time, they suffer from lower DE slope and lower viscosity reduction in secondary liquefaction, where the slurry may be kept at 85-90° C. for up to 90-120 min.
There is therefore a need in the industry for the identification and optimization of amylases and their blends, useful in various production processes, for example, commercial starch liquefaction processes and ethanol production processes.
Low viscosity starch liquefacts are useful in the current ethanol production process. If a way could be found to produce such low viscosity liquefacts as fermentation feedstocks using an optimized blend of alpha-amylases, or variants thereof, this would represent a useful contribution to the art. Furthermore, if a way could be found to treat whole ground grains with a blend of alpha-amylases, or variants thereof, from two different bacterial species to improve starch liquefaction, this would also represent a useful contribution to the art.
A further challenge in the preparation of fermentation feedstocks is that alpha amylases from B. stearothermophilus, for example, have been found to be less effective in hydrolyzing linear amylase, resulting in a retrograded insoluble residual starch under yeast fermentation conditions. The high level of residual starch in the yeast fermentation broth has been considered as one of the major factors influencing the evaporator fouling affecting the downstream processing operations in the ethanol process productions. Thus, if a way could be found to reduce residual insoluble starch in the fermentation broth using an optimized blend of alpha-amylases, or variants thereof, this would also represent a useful contribution to the art.